Radiation therapy is sometimes used to treat cancerous tissue within the human body. During radiation therapy, a radiation source external to the body is aimed at the target tissue to be treated within the body. Due to patient movement during the procedure, the radiation source sometimes misses the target tissue and adversely affects surrounding, healthy tissue. To increase the accuracy of the radiation source and to reduce damage to surrounding tissue, Image-Guided Radiotherapy (IGRT) is sometimes used. In such procedures, the target tissue is marked, either with a skin tattoo or an implantable fiducial marker, and the radiation source is directed towards that marker.
Typically, to implant a fiducial marker into a target tissue, a clinician will load the fiducial marker into either the sharp end (distal end) or the back end (proximal end) of a hollow needle, insert the needle into a delivery system such as an endoscope and maneuver the needle to the target tissue, puncture the target tissue with the needle, and inject the fiducial marker into the target tissue with a stylet. It is often desirable to implant two or more fiducial markers at different locations within the target tissue so that the precise location of the target tissue can be determined through triangulation techniques. Accordingly, after implanting the first fiducial marker, the clinician typically must completely remove the needle from the delivery system, manually reload the sharp end of the contaminated needle with a second fiducial marker, reinsert the needle through the delivery system to reach a different location within the target tissue, and then implant the second fiducial marker with the stylet. In some instances, the entire delivery system is removed from the body each time a new fiducial marker is loaded into the needle. This process is repeated until all of the fiducial markers are implanted.
Repeatedly removing the needle from the delivery system and manually reloading each of the fiducial markers into the needle one at a time may be difficult and cumbersome due to the small size of the fiducial markers and may also increase the duration of the procedure and the risk of injury to both the patient and the clinician. Alternatively, if the clinician instead loads several fiducial markers into the back end of the needle at once, it may be difficult to push the fiducial markers all the way through the needle with the stylet. If the clinician instead loads the fiducial markers into the sharp end of the needle, there is an increased risk of accidental needle stick and disease transmission to the clinician. In any case, when multiple fiducial markers are loaded into the needle, it may be difficult for the clinician to controllably implant a single fiducial marker at a time to achieve adequate spacing between each implanted fiducial marker instead of accidently implanting multiple fiducial markers in one location within the target tissue.